Some basic concepts review 1 What is the

Some basic concepts review 1

What is the Internet? r Terdiri dari jutaan perangkat computing : hosts, end-systems m pc’s workstations, servers m phones, toasters Yang menjalankan network applications r communication links m fiber, copper, radio, satellite r routers: memforward paket data melalui jaringan 2

What is the Internet? r protocols: mengendalikan pengiriman dan penerimaan messages m mis : TCP, IP, HTTP, FTP, PPP r Internet: “network of networks” m loosely hierarchical m public Internet versus private intranet r Internet standards m RFC: Request for comments m IETF: Internet Engineering Task Force 3

What is the Internet: a service view r Suatu infrastruktur komunikasi yang memungkinkan adanya aplikasi terditribusi: m WWW, email, games, e-commerce, database, m more? r Layanan komunikasi yang disediakan: m connectionless m connection-oriented 4

What is a protocol? r Semua aktivitas komunikasi di Internet diatur oleh protokol r Protokol : Aturan-aturan dan perjanjian yang mengatur pertukaran informasi antar komputer di jaringan Protokol mendefinisikan : format, urutan message yang dikirim dan yang diterima oleh entitas jaringan, serta tindakan (action) yang harus diambil bila mengirimkan atau menerima message - mendefinisikan syntax dan semantic 5

What is a protocol? a human protocol and a computer network protocol: Hi TCP connection req. Hi TCP connection reply. Got the time? Get http: //gaia. cs. umass. edu/index. htm 2: 00 <file> time 6

Struktur jaringan r network edge: m hosts m applications r network core: m routers m network of networks r access networks, physical media: m communication links 7

The network edge: r end systems (hosts): m m m Menjalankan program aplikasi mis: WWW, email at “edge of network” r client/server model m m client host mengirimkan request ke server, dan menerima layanan (service) dari server mis : WWW client (browser)/server; email client/server r peer-peer model: m m Interaksi antar host yang simetri mis: teleconferencing 8

Network edge: connection-oriented service Goal: Transfer data antar end systems: r Didahului proses handshaking m Pembentukan koneksi sebelum transfer data dilakukan r Contoh : TCP - Transmission Control Protocol m Internet’s connection-oriented service 9

Network edge: connection-oriented service TCP service [RFC 793] r reliable, in-order byte-stream data transfer m loss: acknowledgements and retransmissions r flow control: m sender won’t overwhelm receiver r congestion control: m senders “slow down sending rate” when network congested 10

Network edge: connectionless service Goal: transfer data antar end systems m no handshaking! r Contoh : UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service m unreliable data transfer m no flow control m no congestion control 11

Network edge App’s using TCP: r HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: r streaming media, teleconferencing, Internet telephony 12

The Network Core r Interkoneksi berbentuk mesh dari sejumlah routers r Pertanyaan mendasar: bagaimana data ditransfer melalui jaringan ? m circuit switching: dedicated circuit per call: telephone net m packet-switching: data dikirimkan dalam bentuk paket-paket 13

Network Core: Circuit Switching End-end resources reserved for “call” r link bandwidth, switch capacity r dedicated resources: no sharing r circuit-like (guaranteed) performance r call setup required 14

Network Core: Circuit Switching network resources (mis. bandwidth) dibagi-bagi r Setiap bagian dialokasikan untuk suatu call r Suatu bagian resource akan idle jika tidak digunakan oleh pemiliki (call) bagian tersebut (no sharing) r Cara membagi bandwidth dari suatu link m frequency division m time division 15

Network Core: Packet Switching Setiap aliran data end-to-end dikirimkan dalam bentuk paket r Paket dari user A dan B memakai secara bersama (share) network resources r Setiap paket menggunakan bandwidth link secara penuh r resources hanya digunakan jika perlu Bandwidth division into “pieces” Dedicated allocation Resource reservation Karakteristik r resource contention: Permintaan pemakaian resource dapat melebihi jumlah resource yang tersedia r store and forward: paket dikirimkan per hop m transmit over link m wait turn at next link r congestion: ada antrian paket 16

Network Core: Packet Switching 10 Mbs Ethernet A B statistical multiplexing C 1. 5 Mbs queue of packets waiting for output link D 45 Mbs E 17

Network Core: Packet Switching Packet-switching: store and forward behavior 18

Packet switching versus circuit switching Packet switching memungkinkan lebih banyak user yang menggunakan jaringan! Misalkan sejumlah user terhubung kepada suatu link 1 Mbit. Bila sedang “aktif”, setiap user mengirimkan informasi dengan kecepatan 100 Kbps. Setiap user aktif N selama 10% dari waktu r Pada circuit-switching: m users 1 Mbps link N=10 users r Pada packet switching: m Dengan N= 35 users, peluang > 10 user aktif lebih kecil daripada. 004 19

Packet switching versus circuit switching Jadi packet switching adalah sang juara ? r Cocok untuk bursty data m resource sharing m no call setup r Memiliki kemungkinan terjadinya kongesti: mengakibatkan ter-delay-nya paket atau bahkan menyebabkan hilangnya paket (loss) m Dibutuhkan protokol congestion control untuk reliable data transfer, r Masalah : Bagaimana menyediakan kualitas seperti pada circuit-switching? 20

Packet-switched networks: routing r Goal: mentransfer paket antar router dari source ke destination r Pada datagram network: m m destination address determines next hop routes may change during session r Pada virtual circuit network: m each packet carries tag (virtual circuit ID), tag determines next hop m fixed path determined at call setup time, remains fixed through the call m routers maintain per-call state 21

Access networks and physical media Bagaimana cara menghubungkan end systems ke edge router? r residential access nets r institutional access networks (school, company) r mobile access networks Important issues: r bandwidth (bits per second) of access network r shared or dedicated 22

Residential access: point to point access r Dialup via modem m up to 56 Kbps direct access to router (conceptually) r ISDN: integrated services digital network: 128 Kbps all-digital connect to router r ADSL: asymmetric digital subscriber line m FDM m up to 1 Mbps home-to-router m up to 8 Mbps router-to-home 23

Residential access: cable modems r HFC: hybrid fiber coax m cable modems m asymmetric: up to 10 Mbps upstream, 1 Mbps downstream r network of cable and fiber attaches homes to ISP router m m shared access to router among houses issues: congestion, dimensioning 24

Institutional access: local area networks r company/univ local area network (LAN) connects end system to edge router r Ethernet: m shared or dedicated cable connects end system and router m 10 Mbs, 100 Mbps, Gigabit Ethernet 25

Wireless access networks r shared wireless access network connects end system to router r wireless LANs: m radio spectrum replaces wire m e. g. , Lucent Wavelan 10 Mbps r wider-area wireless access m CDPD: cellular digital packet data m wireless access to ISP router via cellular network m GPRS 26

Physical Media r physical link: m transmitted data bit propagates across link r guided media: m signals propagate in solid media: copper, fiber r unguided media: m signals propagate freely, e. g. , radio 27

Physical Media: twisted pair Twisted Pair (TP) r two insulated copper wires m Category 3: traditional phone wires, 10 Mbps Ethernet m Category 5 TP: 100 Mbps Ethernet 28

Physical Media: coax, fiber Coaxial cable: r wire (signal carrier) within a wire (shield) m baseband m broadband r bidirectional r common use in 10 Mbs Ethernet Fiber optic cable: r glass fiber carrying light pulses r high-speed operation: m m 100 Mbps Ethernet high-speed point-to-point transmission (e. g. , 5 Gps) r low error rate 29

Physical media: radio r signal carried in electromagnetic spectrum r no physical “wire” r bidirectional r propagation environment effects: m m m reflection obstruction by objects interference Radio link types: r microwave m e. g. up to 45 Mbps channels r LAN (e. g. , wave. LAN) m one to tens of Mbps r wide-area (e. g. , cellular) m e. g. CDPD, 10’s Kbps r satellite m bandwidth in the Gbps range m 270 Msec end-end delay 30

Delay in packet-switched networks Paket-paket mengalami delay pada saat menempuh perjalanan end-to-end r Ada empat sumber delay pada setiap hop (lihat gambar) transmission A r nodal processing: m check bit errors m determine output link r queueing m time waiting at output link for transmission m depends on congestion level of router propagation B nodal processing queueing 31

Delay in packet-switched networks Transmission delay: r R=link bandwidth (bps) r L=packet length (bits) r time to send bits into link = L/R transmission A Propagation delay: r d = length of physical link r s = propagation speed in medium (~2 x 108 m/sec) r propagation delay = d/s Note: s and R are very different quantitites! propagation B nodal processing queueing 32

Queueing delay r R=link bandwidth (bps) r L=packet length (bits) r a=average packet arrival rate traffic intensity = La/R r La/R ~ 0: average queueing delay small r La/R -> 1: delays become large r La/R > 1: more “work” arriving than can be serviced, average delay infinite! 33

Protocol “Layers” Networks are complex! r many “pieces”: m hosts m routers m links of various media m applications m protocols m hardware, software Question: Is there any hope of organizing structure of network? 34

Organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing r a series of steps 35

Organization of air travel: a different view ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing Layers: Setiap layer menerapkan layanan m Melalui tindakan-tindakan yang dilakukan pada layer itu sendiri m Mengandalkan layanan yang disediakan oleh layer yang ada dibawahnya 36

Layered air travel: services Counter-to-counter delivery of person+bags baggage-claim-to-baggage-claim delivery people transfer: loading gate to arrival gate runway-to-runway delivery of plane airplane routing from source to destination 37

ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing arriving airport departing airport Distributed implementation of layer functionality intermediate air traffic sites airplane routing 38

Why layering? Untuk menanggulangi masalah pada sistem yang kompleks: r Struktur yang eksplisit memungkinkan identifikasi hubungan antara bagian-bagian pada sistem yang kompleks r Modularitas memudahkan maintenance dan updating sistem m Perubahan implementasi layanan pada suatu layer transparan terhadap komponen sistem yang lain • mis. , perubahan kebijakan pada prosedur pemeriksaan di airport gate tidak mempengaruhi komponen sistem airline yang lain 39

Open System Interconnection (OSI) Reference Model r Dikembangkan oleh International Organization for Standardization (ISO) pada tahun 1984 r Model referensi OSI adalah suatu model konseptual yang terdiri atas tujuh layer, masing layer mempunyai fungsi tertentu r Setiap layer adalah self-contained fungsi yang diberikan ke setiap layer dapat diimplementasikan secara independent Updating fungsi suatu layer tidak akan mempengaruhi layer yang lain 40

7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical • Upper layers application issues pada umumnya diimplementasikan secara software • Application oriented • Lower layers data transport issues Layer 1 & 2 : h/w & s/w implemented Layer 3 dan 4 : s/w implemented • Network oriented 41

Model OSI dan komunikasi antar sistem Sistem A Proses aplikasi Application Sistem B Proses aplikasi Peer-to-peer communications Presentation Application Presentation Session Transport Network Data Link Physical Intermediate node (repeater, bridge, router) 42

Interaksi antar layer OSI: r Interaksi dengan layer di atasnya r Interaksi dengan layer di bawahnya r Interaksi dengan layer peer di sistem yang berbeda Application Presentation Sistem A Session Transport Application N+1 N N-1 Presentation Session Sistem B Transport Network Data Link Physical 43

Layer dan pertukaran informasi Sistem A Sistem B 7 7 6 5 Protocol Data Unit = PDU Header 4 4 Data 4 enkapsulasi 3 3 Header 3 2 1 Header 2 Data 2 1 Network 44

Internet (TCP/IP) protocol stack r application: mendukung aplikasi jaringan m ftp, smtp, http r transport: transfer data antar aplikasi m tcp, udp r network: merutekan datagrams dari sumber ke tujuan m ip, routing protocols r link: transfer data antar elemen jaringan m ppp, ethernet r physical: pengiriman bit-bit pada medium transmisi application transport network link physical 45

Host A Host B Application identical message Application Transport identical packet Transport Router R Internet N-Interface identical datagram identical frame Physical Net 1 Internet N-Interface identical datagram identical frame Internet N-Interface Physical Net 2 46

Layering: logical communication Setiap layer: r terdistribusi r Setiap entitas menerapkan fungsi layer pada setiap node r Setiap entitas melakukan pertukaran messages dengan peernya application transport network link physical application transport network link physical 47

Layering: logical communication Mis. : transport r Menerima data dari aplikasi r Menambahkan pengalamatan, dan mekanisme pengujian sehingga terbentuk “datagram” r Mengirimkan datagram ke peer layer r Menunggu ack dari peer data application transport network link physical ack data network link physical application transport network link physical data application transport network link physical 48

Layering: physical communication data application transport network link physical application transport network link physical data application transport network link physical 49

Protocol layering and data Setiap layer menerima data dari layer yang berada di atasnya r Menambhakan header untuk membentuk unit data baru r Mengirimkan unit data baru ke layer yang ada dibawahnya source M Ht M Hn Ht M Hl Hn Ht M application transport network link physical destination application Ht transport Hn Ht network Hl Hn Ht link physical M message M segment M datagram M frame 50

TCP/IP & OSI r Dalam terminologi model referensi OSI, TCP/IP protocol suite meliputi network dan transport layers r TCP/IP dapat diterapkan pada bermacam data-link layers (mampu mendukung bermacam implementasi hardware jaringan) TCP/IP OSI 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical 4 Application 3 2 Transport 1 Network inteface IP 51

Host A Host B Application identical message Transport identical packet Internet Protocol identical datagram Net. Interface identical frame Net. Interface Physical Net 52

Internet structure: network of networks r roughly hierarchical r national/international local ISP backbone providers (NBPs) m m e. g. BBN/GTE, Sprint, AT&T, IBM, UUNet interconnect (peer) with each other privately, or at public Network Access Point (NAPs) r regional ISPs m connect into NBPs r local ISP, company m connect into regional ISPs regional ISP NBP B NAP NBP A regional ISP local ISP 53

National Backbone Provider e. g. BBN/GTE US backbone network 54

ATM: Asynchronous Transfer Mode nets Internet: r today’s de facto standard for global data networking 1980’s: r telco’s develop ATM: competing network standard for carrying high-speed voice/data r standards bodies: m m ATM Forum ITU ATM principles: r small (48 byte payload, 5 byte header) fixed length cells (like packets) m m fast switching small size good for voice r virtual-circuit network: switches maintain state for each “call” r well-defined interface between “network” and “user” (think of telephone company) 55

ATM layers r ATM Adaptation Layer (AAL): interface to upper layers m m end-system segmentation/rea ssembly r ATM Layer: cell switching r Physical application TCP/UDP IP AAL ATM physical Where’s the application? r ATM: lower layer functionality only r IP-over ATM: later ATM physical application TCP/UDP IP AAL ATM physical 56